2. What is biotic stress ?
• Damage done to plants by other living organisms like bacteria,
viruses, fungi, parasites, beneficial and harmful insects, weeds,
and cultivated or native plants.
4. • Plant effected by a
disease or which can
accommodate pathogen
Host
• An organism that
produces the disease
Pathogen
• The ability of a
pathogen to infect a
host strain
Pathogenicity
• Capacity of a pathogen
to incite a disease
Virulence
• The inability of a pathogen to
cause or incite a disease
Avirulence
• Strains of a single pathogen species
with identical or similar morphology
• but differ in pathogenic capabilities
Physiological
race
• Strains of a pathogen
classified on the basis of their
virulence to known resistance
genes present in the host
Pathotype
6. HYBRIDIZATION
Recombination of genes of the two
parental nuclei takes place in the
zygote, and the haploid nuclei or
gametes resulting after meiosis are
different both from
gametes that produced the zygote and
from each other.
Thus every diploid pathogen
individual is genetically different from
any other pathogen
even within the same species and
variability of the new individual
pathogens is continued
indefinitely.
e.g., Phytophthora infestans.
9. • The ability of susceptible host plants to avoid attack of
disease due to
• environmental conditions factors, early varieties,
charge in the date of plating, change in
• the site of planting; balanced application of NPK etc
Disease
escape
• The ability of the plants to tolerate the invasion of the
• pathogen without showing much damage. This
endurance is brought about by the
• influence of external characters. Generally, tolerance is
difficult to measure since it is
• confounded with partial resistance and disease escape.
Disease
endurance
or tolerance
10. • When the host does not show the symptoms of disease it is known as immune
• reaction. Immunity may result from prevention of the pathogen to reach the
appropriate
• parts of the host e.g. exclusion of spores of ovary infecting fungi by closed flowering
• habit of wheat and barley
Immunity
• Immediately after the infection several host cells surrounding the
• point of infection are so sensitive that they will die. This leads to the death of the
• pathogen because the rust mycelium cannot grow through the dead cells. This super
• sensitivity (hypersensitivity) behaves as a resistant response for all practical purposes.
• Phytoalexins are specific polyphenolic or terpenoid chemicals and are produced by the
• host in response to the infection by a pathogen
Hypersensitivity:
11. Feature Vertical resistance Horizontal resistance
1. Pathotype – specificity Specific Non specific
2. Nature of gene action Oligogenic Polygenic; rarely oligogenic
3. Response to pathogen Usually, hypersensitive Resistant response
4. Phenotypic expression Qualitative Quantitative
5. Stage of expression Seedling to maturity Expression increases as plant
matures
6. Selection and evaluation Relatively easy Difficult
7. Host pathogen interaction PRESET Absent
8. Commonly used, synonyms Major: gene, race -specific
seedling, monogenic,
Polygenic, race nonspecific,
pathotype-nonspecific,
mature plant,
9. Efficiency Highly efficient against
specific races
Variable, but operates against
all
Vertical
and
Horizontal
Resistance
(Vander
plank)
12. Sources of Disease Resistance;
Disease
Resistance
A known
variety
Germplasm
collection
Related
species
Through
mutations
13. • Disease reactions of most of the
cultivated varieties are documented
• and a breeder may find the
resistance he needs in a cultivated
variety
A known
variety
• When resistance to a new disease or
a new pathotype of a
• disease is not known in a cultivated
variety germplasm collection should
be screened
Germplasm
collection
14. • Often the resistance to a disease may be found in related species and
• transferred through interspecific hybridization.
• Eg. Resistance to stem, leaf & stripe rusts of wheat
Related
species
• Resistance to diseases may be obtained through mutation arising
• spontaneously or induced through mutagenic treatments.
• Eg.
• 1. Resistance to Victoria blight in oats was induced by irradiation with x-rays
or
• thermal neutrons / also produced spontaneously
• 2. Resistance to stripe rust in wheat
• 3. Resistance to brown rust in oats
• 4. Resistance to mildew in barley
Mutation
15. Methods of Breeding for Disease
Resistanceresistance introduction
selection
Hybridization
Budding &
Grafting
Mutation
Breeding
Biotechnological
methods
16. Plant Introduction
Example
Early varieties of groundnut introduced
from USA have been resistant to leaf spot
(Tikka)
135
· Kalyanasona and Sonalika wheat
varieties originated from segregating
material
introduced from CIMMYT, Mexico, were
rust resistant.
· African bajra introductions have been
used in developing downy mildew resistant
cms lines.
17. · Kufri Red potato is
selection from
Darjeeling Red round
· Pusa Sawani behind
(yellow mosaic)
selection from a
collection obtained from
Bihar
· MCU I was selection
from CO4 for black arm
resistance in cotton
SELECTION
18. HYBRIDIZATION
Pedigree
method
In wheat Kalyana
Sona, Sonalaka,
Malvika 12
Malvika 37,
Malavika 206,
Malavika 234
Laxmi in Cotton
(Gadag 1 x CO2) for
leaf blight
resistance
backross
agronomically
highly
desirable variety.
If the resistant
parent is a wholly
unadapted variety,
backcross method
is a logical
choice
19. •The disease resistance in vegetatively propogated
material is
•transferred by adopting either by budding or
grafting. By grafting or budding the resistant
•material, the resistance can be transferred
Budding
&
Grafting
•When adequate resistance is not available in the
germplasm ;
•Mutation breeding is resorted to induce resistance.
This is also us ed to break the linkages
•between desirable resistant genes and other
desirable genes.
Mutation
Breeding
20. VARIETIES RESISTANT TO DIFFERENT
DISEASES
crop variety
Rice : Blast Co25, Co26
Wheat : all three rusts NP 809
Yellow rust NP 785, NM86
Sugarcane : Red rot Co 419, Co 421, Co 527
Cotton : Wilt Vijay, Kalyan, Suyog
Tikka leafspot Ah 45
